This invention relates to the preparation of diether dianhydrides, and more particularly to improved phase transfer catalyzed methods for such preparation.
Diether dianhydrides are important monomers for the preparation of polyetherimides having exceptionally high temperature performance and excellent solvent resistance. These properties are useful in high performance plastics applications such as advanced composites and electronic circuit materials.
A number of publications describe the preparation of diether dianhydrides, none however, discloses the method of the present invention and its advantages. Such publications include U.S. Pat. Nos. 3,956,320, 3,850,964, 4,868,316, and 6,706,897. Suitable reaction conditions for the reaction between halophthalic anhydrides and aromatic dihydroxy compounds include neat and solvent reactions and the presence of various catalysts, typically phase transfer catalysts such as tetraphenylphosphonium halides, fluorides such as potassium fluoride and cesium fluoride and carboxylic acids and their salts and hydrolysable esters. Many of these reactions suffer from low product yields. Moreover, numerous ambiguities are present in said publications regarding water content of the reaction mixtures and other conditions, making reproducibility questionable.
It is of interest, therefore, to provide a direct method for diether dianhydride preparation which affords high yields and a minimum of by-products, and which is consistently and reproducibly applicable.